U.S. Pat. No. 6,869,474 to Perez-Pena et al, incorporated herein by reference, discusses extremely fast setting of cementitious compositions for producing cement-based products such as cement boards achieved by adding an alkanolamine to hydraulic cement such as Portland cement, and forming a slurry with water under conditions that provide an initial slurry temperature of at least 90° F. (32° C.). Additional reactive materials may be included such as high alumina cement, calcium sulfate and a pozzolanic material such as fly ash. The extremely rapid set permits rapid production of cementitious products. The use of expanded clay lightweight aggregates has been found to be a very useful in producing formulations with relatively low weight and high compressive strengths. However, the production of expanded clay aggregte is high energy intensive and depletes natural resources and their use limits the ability to design concrete mixtures at densities in the range of 40 to 50 pcf. Furthermore, the expanded clay aggregate are highly porous materials which tend to absorb the cement paste slurry, thus their relatively high in-situ density.
U.S. Pat. No. 7,670,427 of Perez-Pena et al, incorporated herein by reference, discusses extremely fast setting of cementitious compositions with early-age compressive strength for producing cement-based products such as cement boards achieved by adding an alkanolamine and a phosphate to a hydraulic cement such as portland cement, and forming a slurry with water under conditions that provide an initial slurry temperature of at least 90° F. (32° C.). Additional reactive materials may be included such as high alumina cement, calcium sulfate and a pozzolanic material such as fly ash. Again, all of the compositions contained a significant amount of hydraulic cement and gypsum.
Published US Patent Application No. US 2010-0071597 A1 of Perez-Pena discloses formulations using fly ash and alkali metal salts of citric acid such as sodium citrate to form concrete mixes with fast setting time and relatively high early age compressive strength. One of the challenges encountered with the activated fly ash binders described in this application, is an apparent interaction between these binders and the traditional foaming systems used to entrain air and thereby make lightweight boards. The fly ash based binders which have been made with traditional foams in accordance with this disclosed method have suffered foam collapsing and/or drastic strength reduction. In addition, fly ashes may increase the combustibility of building materials due to the increasingly organic carbon levels as a result of carbon injection during the power plant operations and as a result of recent EPA regulations to limit exhaust emissions into the environment.
U.S. Pat. No. 4,488,909 to Galer et al, incorporated herein by reference, discusses cementitious compositions capable of rapid setting. The compositions permit high speed production of carbon dioxide resistant products by forming essentially all of the potential ettringite within about 20 minutes after the composition is mixed with water. The essential components of the cementitious composition are portland cement, high alumina cement, calcium sulfate and lime. Pozzolans such as fly ash, montmorillonite clay, diatomaceous earth and pumicite may be added up to about 25%. The cement composition includes about 14 to 21 wt % high alumina cement, which in combination with the other components makes possible the early formation of ettringite and other calcium aluminate hydrates responsible for early setting of the cementitious mixture. In their invention, Galer et al provided aluminates using high alumina cement (HAC) and sulfate ions using gypsum to form ettringite and achieve rapid setting of their cementitious mixture.
Ettringite is a calcium aluminum sulfate compound having the formula Ca6Al2(SO4)3.32H2O or alternatively 3CaO.Al2O3.3CaSO4.32H2O. Ettringite forms as long needle-like crystals and provides rapid early strength to cement boards, so that they can be handled soon after being poured into a mold or over a continuous casting and forming belt.
U.S. Pat. No. 5,536,310 to Brook et al disclose a cementitious composition containing 10-30 parts by weight (pbw) of a hydraulic cement such as portland cement, 50-80 pbw fly ash, and 0.5-8.0 pbw expressed as a free acid of a carboxylic acid such as citric acid or alkali metal salts thereof, e.g., tripotassium citrate or trisodium citrate, with other conventional additives, including retarder additives such as boric acid or borax, which are used to accelerate the reaction and setting time of the composition to overcome the disclosed disadvantageous of using a high fly ash content in cement compositions.
U.S. Pat. No. 5,536,458 to Brook et al disclose a cementitious composition containing a hydraulic cement such as portland cement, 70-80 parts by weight fly ash, and 0.5-8.0 pbw of a free carboxylic acid such as citric acid or an alkali metal salts thereof e.g. potassium citrate or sodium citrate, additives like potassium hydroxide with other conventional additives including retarder additives such as boric acid or borax, which are used to accelerate the reaction and setting time of the composition to overcome the known disadvantageous of using a high fly ash content in cement compositions.
There is a need to find a method to reduce the weight of portland cements based binder mixes so these formulations can be used to manufacture lightweight cementitious concrete products for applications such as backer board and other wall or ceiling applications with improved strength without the use expanded clay aggregate. The present method has developed formulations with enhanced compressive strength at reduced weight and with reduced cost.